Lysospholipids such as lysophosphatidic acid (LPA) are implicated in a diverse array of cellular functions including cell proliferation, migration, programmed cell death and differentiation, and have been linked to such health-related concerns as wound healing, atherosclerosis and cancer. Recent reports linking LPA to blood clot formation suggest a potential stimulatory role for this lipid factor in bone fracture healing. The latest evidence by the PI suggests a paracrine signaling function for LPA involving G protein-coupled receptors on the plasma membrane of bone-forming osteoblasts and the subsequent release of intracellular Ca2+ from the endoplasmic reticulum (ER). This application consists of two Specific Aims designed to test our hypotheses that (1) LPA stimulates osteoblast migration and proliferation, and (2) LPA-induced Ca2+ signaling in osteoblasts involves plasma membrane receptors of the Edg family and ryanodine-sensitive Ca2+ channels in the ER. The proposed approach will employ a mouse osteoblastic cell line and rat primary osteoblast cultures to integrate measurements of bone cell function (osteoblast migration and proliferation) with the use of a Ca2+ sensitive fluorescent dye and ribozyme-mediated gene function ablation, a modern technique in molecular genetic manipulation. Among the innovations included in this plan are the application to osteoblasts of principles gained from studies of endothelial cells and platelets, and a novel strategy to enhance Ca2+ signaling in osteoblasts as a means to test hypotheses linking LPA-elicited elevations in cytosolic Ca2+ levels to the stimulation of osteoblast migration and proliferation.